This invention relates generally to apparatus attached to a tracked vehicle for lifting, transporting and laying pipe and is particularly directed to a bulldozer/pipelayer combination having a folding boom and a pair of track roller frames which oscillate when operated in the bulldozer mode and are locked in a fixed orientation when the apparatus is used in pipelaying.
A common approach for laying pipe employs a diesel powered tracked vehicle having a side boom for lifting, transporting and positioning the pipe in or on the ground. The tractor, which frequently is in the form of a bulldozer, includes a primary closed, pressurized hydraulic system for bulldozer operation and a secondary hydraulic system coupled to the first primary system for pipelayer control. The tractor travels generally parallel with the pipeline, with its offset position from the pipeline determined by operating conditions and the size and characteristics of its side boom.
The typical bulldozer includes a front blade or scoop for moving soil or heavy objects and a pair of side-mounted track roller frames each supporting a respective endless track for propelling the bulldozer. The track roller frames are attached to the bulldozer""s main frame in a pivoting manner which allows the track roller frames to oscillate up and down about a horizontal axis passing through the main frame. The vertical displacement of the forward and aft portions of each of the track roller frames as the bulldozer traverses irregular terrain provides better traction and grading characteristics, as well as a more comfortable ride for the operator. When a pipelayer is attached to the bulldozer and used in the laying of pipe, the vehicle""s main frame is positioned to the side of the pipe which is maneuvered into position as the vehicle moves forward. In a conventional pipelayer, the track roller frames are rigidly attached to the vehicle""s main frame and are not free to pivot in an oscillating manner. This provides the pipelayer attachment with a more stable platform for lifting and transporting heavy loads, but limits the use of the tracked vehicle as a bulldozer because the track roller frames are locked in a fixed position on the vehicle""s main frame.
A pipelayer attachment typically includes a boom structure pivotally attached to one of the track roller frames of the tracked vehicle and extending to one side of the vehicle. A boom and load winch combination allows the boom structure and a load supported by the boom structure to be raised or lowered. When retracted for transport or storage, the boom structure assumes a generally vertical orientation and extends well above the height of the tracked vehicle. This limits where the tracked vehicle may be transported and stored. In order to avoid this problem, the boom structure is sometimes removed from the tracked vehicle frame for transport and/or storage, but this removal and subsequent reattachment is cumbersome, time consuming and requires several workers. In addition, when the tracked vehicle is used as a bulldozer, the retracted or upraised boom structure limits where the bulldozer can be operated.
The present invention addresses the aforementioned limitations of the prior art by providing a bulldozer/pipelayer combination incorporating a folding boom structure which can be extended for use or retracted for transport, storage or when bulldozing to a compact configuration disposed in closely spaced relation to the tracked vehicle by the vehicle operator using pipelayer boom and load controls. The bulldozer""s oscillating track roller frames are automatically locked in fixed position on the vehicle""s main frame for use in the pipelaying mode by the operator.
Accordingly, it is an object of the present invention to provide a bulldozer/pipelayer combination that is equally adapted for grading and earth moving as well as for lifting and transporting heavy loads when used in pipelaying.
It is another object of the present invention to provide in a bulldozer with a pipelayer attachment a selectable control for allowing the bulldozer""s track roller frames to oscillate up and down when used as a bulldozer, or for locking the track roller frames in fixed position when operated in the pipelayer mode to provide a stable platform for lifting and transporting heavy loads.
Yet another object of the present invention is to provide a folding boom for a pipelayer attached to a tracked vehicle which can be moved between a folded and an extended position by the vehicle operator using controls employed in the operation of the pipelayer.
A further object of the present invention is to provide a folding pipelayer boom attached to the side of a tracked vehicle which when retracted allows the tracked vehicle to operate in low, narrow areas and permits tracked vehicle transport and storage without removing the boom.
A still further object of the present invention is to provide improved load control in a pipelayer attached to a tracked vehicle such as a bulldozer by rendering the pipelayer""s boom and load winches equally responsive to hydraulic control inputs.
This invention contemplates a bulldozer/pipelayer apparatus comprising a main frame incorporating an engine for driving the bulldozer/pipelayer combination; first and second track roller frames each coupled to a respective lateral portion of the main frame and including a respective segmented, endless track for displacing the apparatus; a boom winch having a boom cable dispose thereabout and a load winch having a load cable disposed thereabout; and a folding boom having first and second frames pivotally coupled together, wherein the first frame is pivotally coupled to the first track roller frame and the second frame is coupled to the boom cable for raising and lowering the boom and is further coupled to the load cable for raising and lowering a load, and wherein the boom is adapted for movement between an extended, use configuration for raising and lowering a load wherein the first and second frame are in generally linear alignment and a folded configuration for storage or transport wherein the first and second frames are aligned generally transverse and are each disposed in closely spaced relation to a side of the apparatus.